fix: v3.0→HEAD review 修复 — handler 注册 + review verdict + skill 全文注入

基于庞统+司马懿背靠背 review，修复 6 个问题：

P0 致命：
- A1: _legacy_on_complete 补回 review verdict 处理（approved→done，非 approved→@mention assignee）
- A2: 添加 TaskTypeRegistry.register() 启动初始化（注册 Task/Mail/Toolchain handler）

P1 中等：
- B11-1: RoleSkillSection 从索引提示改为全文注入（对齐设计 §2.3 + BootstrapBuilder 行为）
- A8: retry prompt is_mail 硬编码改走 TaskTypeRegistry handler 判断

P2 低：
- _mail_* 4 个方法添加 DEPRECATED 注释
- ticker.py handler check_completion 代码块缩进对齐（28→24 空格）

测试：394 passed, 0 failed
Review reports: docs/design/review-v3-vs-head-{pangtong,simayi}.md

src/daemon/spawner.py

@@ -1125,9 +1125,10 @@ curl -X POST http://{api_host}:{api_port}/api/projects/{project_id}/tasks/{task_
         # 构建续杯 message(Mail 用专用模板,Task 用标准模板)
         task_info = self._get_task_info(db_path, task_id) or {}
         project_id = task_info.get("project_id", "")
-        is_mail = project_id == "_mail"
+        handler = TaskTypeRegistry.get_by_project(project_id)
+        is_handler = handler is not None
 
-        if is_mail:
+        if is_handler:
             must_haves = task_info.get("must_haves", "{}")
             try:
                 meta = json.loads(must_haves) if must_haves else {}